ST5000 Mark II Telemetry

Change Log
Version Date Comments
1.0 11-Jun-2003 Initial Release
1.1 24-July-2003 Add Shim Angles
1.2 03-Sep-2003 Improve multi-byte items
1.3 09-July-2004 Fix clock info
1.4 18-Jan-2007 Tabularize, no other changes

This section describes the telemetry packet that is sent out on the serial line.

Notes on the packet layout.

158 bytes (this includes the packet protocol bytes) at 10 Hz requires a comm bandwidth of 12640 bits per second.

The data bytes are encapsulated with sync bytes and a data length according to the ST5000 XMSG protocol.

The packet contains 1, 2, and 4-byte unsigned integers and 4-byte floating point values. The values are encoded (serialized) in big-endian order. The encoding is compatible with the XDR standard. We wrote our own XDR-compatible codec in C and Java; here is the C version, in PDF and source code.

How to read the packet layout.

Frame depth: The ST5000 telemetry is modelled as a NASA-style "major frame" with a depth of 8 minor frames and a minor frame length of 153 slots. Most items have a subcom depth of 1; they repeat each frame. The subcom-8 items are broken out in separate tables.

Frame rate: The ST5000 sends frames during each frame grab, which by default happens at 10 Hz. The 8-frame depth means that the frame repeats in 0.8 seconds. If you change the exposure time, you also change the telemetry frame rate. If you set the exposure time to 15 video frame periods (0.5 s), then the telemetry slows down to 2 Hz.

Here is a brief desciption of each item.

ST5000 Mark II Telemetry
Byte Item Comment
-5 Sync 1 0x4a
-4 Sync 2 0x57
-3 Sync 3 0x50
-2 Length 1/2 See the XMSG Protocol
-1 Length 2/2
0 Routing Code 8 (ST5000 MkII)
1 Packet Code 0 (MkII Telemetry)
2 Frame Number 1/2 (frame % 8) gives the index into the major frame
3 Frame Number 2/2
4 Clock 1/4 UTC seconds since 1970
8 CSR 1 Control Status Register 1
9 CSR 2 Control Status Register 2
10 Digital Inputs
11 Digital Outputs
12 ADC Channel 0 1/2 channel = (frame%8)
14 ADC Channel 8 1/2 channel = (frame%8)+8
16 DAC Channel 0 1/2 Digital to Analog Converters
18 DAC Channel 1 1/2
20 DAC Channel 2 1/2
22 DAC Channel 3 1/2
24 Software Status 1/4
28 RAM A Status 1/2
30 RAM B Status 1/2
32 ACQ State
33 LIS State
34 PIT State
35 Various 1-byte subcommed items
36 Alignment and Calibration items
40 Offsets and Angles
44 ST5000 Yaw Floating point radians
48 ST5000 Pitch Floating point radians
52 ST5000 Roll Floating point radians
56 ACS Yaw Floating point radians
60 ACS Pitch Floating point radians
64 ACS Roll Floating point radians
68 Guide Star Magnitude Floating point V-Magnitude
72 Lost-in-Space items
76 Acquired X-position 1/4 Floating point pixels
80 Acquired Y-position 1/4 Floating point pixels
84 Acquired Peak Value Counts, 0-255
85 Acquired Mode Most common value in the track box
86 Acquired Flux 1/2 Sum of pixels in the track box
88 Catalog ID 1/2 From Lost-in-Space solution
90 Votes 1/2 From LIS solution
92 Current X-position 1/4
96 Current Y-position 1/4
100 Current Peak Value ADUs
101 Current Mode Most common pixel value
102 Current Flux 1/2 ADUs
104 Track box row 1 unsigned bytes
111 Track box row 2 unsigned bytes
118 Track box row 3 unsigned bytes
125 Track box row 4 unsigned bytes
132 Track box row 5 unsigned bytes
139 Track box row 6 unsigned bytes
146 Track box row 7 unsigned bytes

Various 1-byte subcommed items
Minor Frame Item Comment
0 nframes exposure time, in units of video frames. 3 is 10 Hz.
1 shutter shutter value
2 cgain Camera gain (0 = high, 255 = low)
3 track start start here in the list of 32 acquired stars
4 track count track this many
5 track target used as boolean; move to guide star, or just hold steady?
6 nacq number of stars acquired
7 ntrk number of stars still being tracked

Alignment and Calibration items
Minor Frame Item Comment
0 ST5000 Yaw Mechanical Alignment
1 ST5000 Pitch Mechanical Alignment
2 ST5000 Roll Mechanical Alignment
3 Yaw Window Mark VI ACS Outputs
4 Pitch Window Mark VI ACS Outputs
5 Roll Window Mark VI ACS Outputs
6 Magnitude Window Mark VI ACS Outputs
7 - slot 36 Magnitude zero-point (1/2) Sky Calibration
7 - slot 37 Magnitude zero-point (2/2) -
7 - slot 38 Magnitude Offset (1/2) Mark VI ACS Outputs
7 - slot 39 Magnitude Offset (2/2) -

Offsets and Angles
Minor Frame Item Comment
0 Target Yaw Blind Offset Request
1 Target Pitch Blind Offset Request
2 Target Roll Blind Offset Request
3 Guide Star Yaw Offset of guide star
4 Guide Star Pitch Offset of guide star
5 Shim Yaw Shim Angle to ACS Null
6 Shim Pitch Shim Angle to ACS Null
7 Shim Roll Shim Angle to ACS Null

Lost-in-Space items
Minor Frame Item Comment
0 Quaternion Element 1 4-byte floating point
1 Quaternion Element 2 4-byte floating point
2 Quaternion Element 3 4-byte floating point
3 Quaternion Element 4 4-byte floating point
4 Quaternion Eigenvalue 4-byte floating point
5 Plate Scale N/A
6 - slot 72 Triangle Count (1/2) -
6 - slot 73 Triangle Count (2/2) -
6 - slot 74 Cross Tab Count (1/2) -
6 - slot 75 Cross Tab Count (2/2) -
7 spare -